1. Field of the Invention
The present invention relates to an autoxidatively drying alkyd composition containing an emulsifier in the form of a curing alkoxylate of a monoethanolamide.
2. Description of the Related Art
Alkyds have long been used as binders in paints and lacquers, and are employed in both professional and hobby painting, as well as in industrial lacquering. They may be the only binder used, as in air-drying paints, or be combined with e.g. amino resins, as is common in many stove-curing systems.
Alkyds are produced by condensation of a polybasic acid, a polyefunctional alcohol and a fatty acid. The polyfunctional components form the coherent polymer skeleton, and the fatty-acid residues settle as tails on the skeleton. Polyunsaturated fatty acids yield autoxidatively curing, i.e., air-drying, binders, whereas saturated and only slightly unsaturated fatty acids yield alkyds for stove-curing.
Even today, alkyds constitute the binder that is most commonly used in paints and lacquers. In recent years, however, environmental and health reasons have made it desirable to change from hydrocarbon-base to water-base paints, and the alkyd paints have thus lost market shares to latex paints, i.e., paints based on emulsion-polymerised binders, such as polyacrylate and polyvinyl acetate. This change has been especially pronounced in professional painting where the painters' health has always been a major problem. Thus, it is mainly the autoxidatively curing alkyds that have been affected. The solvent currently used in such paints is white spirit.
Thus, the alkyd manufacturers have tried to adapt themselves to this development by making emulsions of alkyds. Accordingly, the alkyd is first produced in conventional manner, and is then emulsified in water. This requires the presence of a surface-active agent, usually in a content of 0.5-4% by weight of the finished paint. The surface-active agent acts as emulsifier, i.e., it contributes to the formation of droplets of the disperse phase and it stabilises the structure by forming, on the droplets, an elastic surface film which reduces the tendency towards coalescence. With the right emulsifier, alkyd emulsions of long storage life can be obtained. Surface-active agents commonly used for this purpose are alkyl phenol ethoxylate and alcohol ethoxylate having HLB values in the range of 8-15. The HLB value (Hydrophilic Lipophilic Balance) is often used for indicating the amphiphilic nature of a surface-active agent.
The use of alkyds in emulsion systems eliminates the hazard of hydrocarbon emission from paints, but at the same time creates other inconveniences for the user.
The emulsifier acts as an external plasticiser in the film of paint. Being surface-active and low-molecular, the emulsifier migrates to the air-paint film of the interface, where it accumulates. As a result, the film becomes softer and its water and chemical resistance is impaired compared with a conventional white-spirit-base paint based on the same alkyd as the binder. Also, the presence of a surface-active agent tends to impair the clarity and gloss of the film, as well as its drying qualities.
Besides the development towards emulsion-base alkyd paints, intensive efforts are being made to produce micro-emulsions of alkyds and use these thermodynamically stable solutions as raw material. Thus, microemulsions constitute an alternative to emulsions when alkyds are to be introduced in a water-base system. Microemulsions differ from emulsions by being thermodynamically stable, i.e., having no tendency to separate when stored, which is a major advantage. However, the production of a microemulsion requires a much larger amount of surface-active agent than does the production of an emulsion. Thus, the emulsifier problems in the form of impaired film properties and reduced drying rate are especially pronounced in the case of alkyds used in paints.